This invention relates to polymeric flow and impact modifiers for polyvinyl chloride (PVC) resin, and to novel PVC compositions. More particularly, the invention relates to particular graft copolymers (ASA) prepared by an emulsion/suspension process wherein acrylonitrile and styrene are polymerized in the presence of poly(butyl acrylate) as polymeric flow and impact modifiers for PVC, and to novel blends of particular ASA graft copolymers with PVC.
Blends of emulsion prepared graft ASA copolymers with PVC are disclosed in U.S. Pat. No. 3,041,307. Such PVC blends have good weatherability and good impact strength, but have undesirable melt flow. The emulsion/suspension prepared ASA copolymers of this invention impart substantially improved flow properties to blends with PVC while maintaining the good impact properties of ASA/PVC blends.
Polyvinyl chloride resins are commonly fabricated from powders or pellets by thermal processes including extrusion and injection molding, during which the particles must be fused into a molten mass. In conventional processing, the fusion and subsequent processing is aided by incorporation of plasticizers. These plasticizers also improve the flow and shear characteristics of the PVC resins by reducing the melt viscosity, thus enhancing the overall processability. Plasticizers, however, are not entirely satisfactory for many purposes inasmuch as they materially reduce the rigidity and heat distortion temperature of the resin when employed in amounts sufficient to improve melt flow.
A further method for improving processability has been to employ a blend of PVC with a second polymeric resin together with a monomeric plasticizer to compatibilize the blend. The second polymeric resin, for example, may be a block copolymer having both rigid and rubbery segments, such as those disclosed in U.S. Pat. No. 3,801,529. The use of large amounts of plasticizer in these compositions again reduces rigidity and the heat distortion temperature of the resin. It is desirable, therefore, to provide a processing aid which can be blended with a PVC resin to improve processability of the resin without a major decrease in the heat distortion temperature of the product composition.